There are two basic approaches available to designing glucose sensor devices that do not suffer from the effects of haematocrit interference. Either the haematocrit of the sample can be measured independently of the glucose measurement, and the glucose measurement is then corrected by a predetermined factor for the measured haematocrit, or the sensor and/or its operation are designed in a way that the glucose measurement is not substantially affected by the haematocrit of the sample in the first place so as to provide a more haematocrit independent measurement. To measure haematocrit and glucose separately, and then correct the glucose measurement using the haematocrit measurement, relies on accurate haematocrit measurement being possible, or else more error may be introduced into the result than is removed.
The simpler method is to devise an haematocrit independent measurement system.
WO2008040998 CARDOSI et al describes applying a plurality of voltages over respective durations to correct for heamatocrit. The analysis used appears somewhat complex. Application of a reverse potential for fill detection is described.
U.S. Pat. No. 6,576,117 IKETAKI describes application of a predetermined voltage twice to promote an electrochemical reaction and correct for errors. The analysis used appears somewhat complex.
WO2012035297 CRAGGS et al describes haematocrit compensation by estimating haematocrit corrected analyte concentration from first, second, third, fourth and fifth test currents. The analysis used appears somewhat complex.
WO2007013915 WU et al describes gated amperometric pulse sequences to provide shorter analysis time and/or improved accuracy and/or precision of analysis.
U.S. Pat. No. 7,288,174 CUI describe using water soluble fatty acid to reduce the haematocrit level dependent bias and US2005/000808 CUI describes an electrochemical biosensor.
Further art includes US2014/0027312 and WO2014/016578 both to MACFIE, (published after the priority date of this application), WO2013/164632 MCNEILAGE, (published after the priority date of this application), US2010/0258451 ADLASSING, WO2012/084194 BURKE, EP2138841 HODGES, US2008/000780 TONKS, GB2296333 MATTHIESSEN, US2004/0260511 BURKE, EP0396788 KUYPERS, U.S. Pat. No. 6,413,398 GERHARDT and US2013/098776 HSU, EP2098857 CHATALIER, EP2042865 CHATALIER, WO2007/121111 POPOVICH, EP1840219 CHATALIER, WO01/57519 O'HARA.
The above art describes examples of both approaches. None are very satisfactory, being too complex and/or requiring adaptation of manufacturing processes. There is therefore a need to provide a simpler approach to mitigation of the effects of haematocrit. Furthermore there is an ongoing need to provide improved haematocrit independent measurement systems and mitigation methods that more accurately reduce the effect of or account for haematocrit level dependent effects in sensor device responses.
The present invention seeks to alleviate one or more of the above problems. Further, the invention aims to provide, in one or more embodiments, a method (and apparatus, metering device, sensor device and kit) for measurement of analyte concentration that is more independent of haematocrit concentration than the prior art and, in particular embodiments, is preferably largely independent of haematocrit concentration, or, more preferably, substantially independent of haematocrit concentration.